1. Field of the Invention
The present invention relates to a pressure display apparatus suitable for use with pressure gauges having a reference point adjustment means for adjusting the display on the display for a given reference pressure value.
2. Description of the Related Art
Generally, the digital pressure gauge for gauge pressure measurement eventually fails to read zero upon exposure to the atmosphere (the zero point) because of changes over time in the pressure sensor and its amplifying circuit. This problem is inevitable even in those having a temperature compensation function.
Therefore, such pressure gauges have a zero reset function, in other words a zero adjustment function to read zero on the display under no pressure (upon exposure to the atmosphere). For example, Japanese Patent Publication No. 11 (1999)-281513 discloses a pressure gauge with a zero-fluctuation cut-off function in which a specific range of fluctuation in the pressure is cut off to stabilize the zero point upon exposure to the atmosphere because a differential pressure type digital pressure gauge requiring a high accuracy (0.03% FS) uses a highly sensitive pressure sensor and the pressure value tends to fluctuate due to slight changes in the pressure upon exposure to the atmosphere, which makes pressure zero point adjustment difficult.
However, the prior art pressure gauge (pressure display apparatus) has the following problems.
First, the prior art zero reset function is operated under no pressure (upon exposure to the atmosphere). It is difficult or not easy to expose the pressure gauge to the atmosphere in view of the nature of objects in which the pressure gauge is installed. In such a case, some drawbacks in universality or flexibility are observed; the zero reset function does not substantially work or the zero reset function is operated on limited occasions such as full inspection during which the operation of the detection object is totally stopped.
Second, the pressure gauge usually does not have a complete linearity from zero to the maximum detection pressure. Even if the pressure gauge is zero-adjusted by the zero reset function, it is uncertain that the pressure gauge is correctly adjusted for pressures to be actually detected. The prior art zero reset function is not perfect in view of benefits and convenience in practical use. Some other problems also remain to be solved.